Participatory research with carers: A systematic review and narrative synthesis

Abstract Introduction As patient and public involvement (PPI) in research has become increasingly common, research‐based recommendations on its principles and impacts have been established. The specifics of conducting PPI are likely to differ when involving different groups. Family/informal carers for those with health conditions or disabilities have a lot to contribute to research, but instances of their involvement have yet to be reviewed. Objective To systematically review and synthesize studies where family/informal carers have been involved in the research process, to develop an understanding of the benefits, barriers and facilitating factors. Methods A search of five electronic databases was conducted using a combination of terms relating to carers, involvement and research. A grey literature search, expert consultation and hand‐searching were also used. Following screening, data extraction and quality assessment, a narrative synthesis incorporating thematic analysis was conducted. Findings A total of 55 studies met the inclusion criteria, with diverse design and participatory approaches. Four themes were identified, relating to the outcomes, challenges, and practicalities of involving carers: (re) building relationships with carers; carers as equals not afterthoughts; carers have unique experiences; carers create change. Full involvement throughout the research was not always possible, due to barriers from the research world and responsibilities of the caring role. The literature demonstrated ways for carers to contribute in ways that suited them, maximizing their impact, while attending to relationships and power imbalances. Conclusion By summarizing the reported instances of carer involvement in research, this review brings together different examples of how successful research partnerships can be built with carers, despite various challenges. Carers are a heterogeneous group, and participatory approaches should be tailored to specific situations. Wider understanding of the challenges of conducting empowering research with carers, and the resources required to address these, are needed. Patient and Public Involvement The initial findings and themes were presented to a group of carers who had been involved in research and whose reflections informed the final synthesis.


| Search strategy and study selection
Systematic searches were conducted from inception until December 7 2021, then updated on March 6 2023.A comprehensive search combined sets of terms relating to (1) carers, (2)   collaboration and (3) research (see Supporting Information S1 for full search narrative).As recommended in other reviews of participatory research, 33 this review included a wide search strategy, searching five databases (Ovid MEDLINE, Ovid Embase, PsycINFO, CINAHL and Web of Science), grey literature (National Institute of Health Research [NIHR], NHS Evidence and PCORI databases), back-referencing, and approaching experts in the field.References were collated on Endnote then uploaded in Rayyan for screening.The first 10% of titles/abstracts were independently screened by two researchers (B.B., M. A.) with 91.6% agreement, and discrepancies were discussed with supervisors (V.L., C. H.), before B. B. screened the remaining titles/abstracts.This process was repeated for the full-text screening (agreement 80%).Authors were contacted for missing eligibility information before exclusion.Once an example of carer involvement was identified as eligible, associated publications were collected for data extraction.

| Eligibility criteria
In accordance with the commonly used definition of public involvement as conducting research with rather than on or for, 38 we excluded studies where carers only contributed as passive participants to the data.To select only higher levels of involvement, one-off consultations were excluded.Moreover, studies where carers were only involved in priority-setting, guideline development or intervention codesign were excluded due to our focus on involvement in the research process (despite the important contributions they can make to these stages).Only studies where carers, defined as those informally supporting someone with any health difficulty or disability, 39 were the majority of public contributors were included.
Each instance had to have available description of the participatory approach, research process and results, although this could be reported in multiple publications (full eligibility criteria Table 1).

Study design Research exclusion
• Intervention design only Studies where there is no details of the participatory approach or outcomes of this a Defined as any method where participants have ownership over the direction and process of data collection, and the meaning making.These can include social mapping, body-mapping, theatre, photovoice. 40

| Data extraction
Characteristics of the studies (e.g., population, methods), details of carer involvement, and outcomes and practicalities of this involvement (extracted verbatim), from all primary papers and their associated references were extracted into an Excel spreadsheet (example in Supporting Information S2).The absence of details was recorded as 'not reported'.For the first six studies, this was completed by two researchers independently (B.B., V. L.), discussed and clarified, before the table was applied to the remainder by B. B.

| Quality appraisal
The Mixed-Methods Appraisal Tool (MMAT) 41 was used to assess the quality of the research.As advised by its authors Hong et al., 41 total scores were considered with regard to the importance of individual items in context to the study, to determine whether the research methods were 'high/medium/low' quality.Where a team of carers and researchers had conducted multiple studies, each was assessed separately, with reference to all available reports.Two researchers independently rated 10 studies (78.5% agreement), and discrepancies were discussed (B.B., S. A. K.), before B. B. assessed the remainder.
These appraisal tools may not capture studies with ideological underpinnings, nor do they reflect the quality of participatory processes.There is no standardized tool to appraise participatory approaches, so the 'Critical Appraisal Guidelines for assessing the quality and impact of user involvement in research', 9 which claims to apply to diverse rationales, was selected.This was applied to the primary paper describing the participatory approach.Again, scores were considered in the context of the importance of individual items, to inform an overall categorization of 'high/medium/low' for the quality of what was reported about the ways carers were involved.

| Data analysis and synthesis
A narrative synthesis approach 42 was selected, as it suits reviews with diverse studies, allowing both a description of the research field and exploration of the implementation considerations.The approach has four key elements; (1) developing a theory of how the intervention works, (2) preliminary synthesis of findings, (3) exploring relationships between studies and (4) assessing the robustness of the synthesis.
A multitude of theoretical frameworks for participatory research 30 have been proposed, but given the diversity incorporated in this review, one single theory was not applicable.Data extraction was limited to and mapped onto the research questions, then data T A B L E 2 Summary of participatory approaches according to 'The Levels and Stages'. 43equency (n = 55) Highest level of involvement Research topic, design, data collection, data analysis and dissemination.
Abbreviation: PPI, public and patient involvement.a Total is more than 55 because some studies applied multiple forms of involvement within their approach.
was analysed to iteratively develop general recommendations for carer involvement across contexts.
The preliminary synthesis incorporated summary tables of study characteristics, a thematic analysis across studies, and discussions of the findings with three carers who had extensive experience of PPI.
For the thematic analysis, verbatim data on the outcomes and practicalities of the participatory approaches was collated on NViVo.Finally, the quality of all the included studies, the robustness of this review method, and discussions of whether the review's findings corresponded to the experiences of carers from the NIHR steering, informed reflection on the credibility and trustworthiness of the narrative synthesis conclusions (explored in Discussion).

| Search and screening results
The initial search identified 8195 records; a further 157 were identified through backward reference searching and recommendations of experts (see Figure 1).Following deduplication, 5217 went through to the title/abstract screening.

| Context, characteristics and quality of research methods and participatory approaches
See Table 3 for details of the included papers.Most studies were conducted in higher income countries; photovoice was conducted in South Korea, 45 Peru, 46 Malawi 47,48 and Kenya, [49][50][51][52] as well as with migrant and indigenous communities.Sixteen studies were judged to use only consultative methods (Figure 3).
High quality involvement was less common than high quality research methods (Figure 2).High quality research was most common amongst studies that also showed high quality participatory approach.Absence of appropriate training for carers, discussion of ethical issues relating to involvement, or evaluation of participatory approach, were amongst the common weaknesses (Figure 3).Many studies did not provide a rationale for using a participatory approach or show how carer involvement 'added value' (see Supporting Information S4 for full scoring).

| Thematic analysis and lived experience reflections
Four overarching themes were identified relating to the benefits, barriers, and facilitating factors for the involvement; (re)building relationships with carers, carers as equals not afterthoughts, carers have Distribution of quality of research methods using MMAT, 41 according to quality of participatory approach using 'Critical appraisal guidelines'. 9MMAT, Mixed Methods Appraisal Tool.
unique experiences, and carers create change (see Supporting Information S5).Many of the subthemes resonated with the carers from the NIHR steering groups' experiences, but there were also elements they felt were missing from the literature or needed more emphasis.

| (Re)building relationships with carers
Conducting participatory research in relationship-focused ways was particularly relevant to working with carers, to navigate the challenges of 'perceived hierarchical differences between professionals and family carers, and family carer predominantly negative perceptions', 62,p.805 and bring together difference. 24,145Authors described various facilitators of successful relationships.Additional time was needed to connect with carers as individuals, 118 through frequent communication 74,114 and small, regular and informal meetings. 99Collaboratively establishing working agreements at the start 122,124 and constantly reviewing these together 55 was recommended.'Researchers taking action when they said they would' 111,p.4 or transparency when this was not possible, 126 was helpful to build trust with carers, as was demonstrating long-term commitment, 32 continuity, 137 and connecting with carers' communities 114 during the research.
Trusting relationships were a key ingredient to successful participatory research, resulting in increased openness, 107 'two-way growth', 55,p.1227 and engagement of the wider community in research. 70,71Reports of studies where carers were involved in fewer stages of the research tended to pay less attention to building relationships.Carers from the NIHR steering group pointed out that while trust and respect are essential for all public involvement, they have increased relevance to carers, who often have negative experiences of health services that can create barriers to research relationships.

| Carers as equals, not afterthoughts
The pressures and requirements of academia often limit the extent carers could be involved in the research.Barriers included complex bureaucratic structures, for example, the lengthy process of acquiring security checks required for carers' research access created long delays and additional work for carers and researchers. 32Similar frustrations were echoed in the NIHR steering group.These difficulties are likely to deter researchers and carers from involvement in certain stages of the research, particularly data collection.
Resource constraints were another frequent explanation for making pragmatic adaptations to best practice participatory involvement. 94,111,152Decisions were frequently made before carers became involved, commonly due to the requirements of funders or ethics committees. 80,147p.23This experience was also shared by carers from the NIHR steering group who felt their involvement was treated like a 'they said, we did' tick-box exercise.p.23This may result in hesitancy amongst carers to contribute or offer criticism. 147Carers from the NIHR steering group suggested this risk was particularly relevant with carers, who may Percentage of participatory approaches evidencing each criteria of quality in 'Critical appraisal guidelines'. 9ave experienced feeling diminished by healthcare professionals previously overruling or overlooking them.Finally, this review found that the majority of studies did not involve carers from diverse backgrounds. 78,154Some studies (particularly participatory action research [PAR]) specifically focused on working with marginalized groups, but the measures to broaden access and inclusion proved costly 95 and often required years of sustained community partnership. 47pers described their efforts to work in more equitable ways with carers.Making the research accessible enabled meaningful contributions, 143 e.g.presenting information in multiple formats and providing appropriate training. 107Researchers attended to power imbalances, 70 for example, by disclosing their own personal experiences, 111 or ensuring carers chaired/represented the majority in meetings. 64Establishing clear roles and expectations before involvement and being flexible in following carers' agendas 80 gave carers more control during the process.p.4This also reduced the imposition of researcher values on data.When describing their experiences of involvement in research, the carers from the NIHR steering group noted that like with other marginalized groups, it was crucial to give space to be listened to, rather than dictating the agenda and expecting carers to talk about what was 'relevant', was crucial.
Demonstrating that researchers valued the expertise of the carers 90 through timely payment 99 was key, particularly as much of the caring support they provide is unpaid.p.4Institutional support, such as supervisory and funding structures to provide adequate resources, 66 having a whole team understanding of participatory research, and involvement of senior members, further lent importance to carers' roles in research, 111,p.7 and also facilitated the process.
Papers dedicated solely to reflecting on carer involvement seemed more likely to describe themes of power dynamics or the challenges arising.While such papers have more space to discuss these issues, they were also more common when carer involvement had occurred in more stages of the research and through collaboration or control, and more frequently had carers as coauthors.When carers contributed to the writeup, papers showed more in-depth exploration of all the themes (relationships, power, carer issues, and change).Carers from the NIHR steering group wondered whether there would be differences in the participatory approaches of newer studies, but the only apparent pattern seemed to be an increase in coauthorship in the last 10 years.

| Carers have unique experiences
A prominent theme in the literature was that the insight of the carers informed and improved the research.This was especially evident where carers contributed at the design and analysis stages. 32Early input ensured the relevance of the research, 94 for example, carers identified which measures were important to them and their families. 126Studies claimed to have more ethical rigour, 57 as carers highlighted potentially sensitive issues 75 and suggested more appropriate support strategies, 138 wording and methods. 65,136Their understanding of the participants increased the efficacy of recruitment methods, 65,66,111 and feasibility of participation to improve retention rates. 95,105p.225Carers also identified key messages and additional implications for practice. 80,113,126An important caveat was that 'there is not a single view held by carers but multiple perspectives', 24,p.89 which cannot be represented by one carer, something emphasised in consultation with the NIHR carers' steering group.Therefore, multiple carers should be involved.
Only one paper compared the quality of the data generated with carer involvement to that of researchers alone. 32This study found that participants actually spoke less openly when they were interviewed by carers as opposed to professionals.The authors suggested that the carers may lack confidence in interviewing, prompting them to question whether the intense resources required to provide adequate training could be more effectively spent at other stages of the research.However, other research studies claimed that participants who were carers felt safer to disclose more with carer researchers. 71,143In these instances, carers cofacilitated interviews/ focus groups with academics, highlighting the need for additional support during this stage and the benefits that can result from pairing both professional and caring experience in the research process.
The helpful insight carers brought was partly due to an increased awareness of some of the challenges carers may face, which also affected them during their involvement in research.For example, caring schedules, 147 transport difficulties and feelings of guilt, 97 hindered carer attendance of meetings. 83p.810Strategies for managing some of these challenges included involving multiple carers for when some could not attend, 24 or had to leave the project, 67 and this also reduced the burden and likelihood of carer burnout. 83Given the fluctuations in the demands of caring, researchers extended the research schedule 97 or created roles with more flexible commitment. 147Due to carers' limited time, it was recommended to 'optimise the consumers input in a timely way' 138,p.649by focusing on tasks in which carers can efficiently contribute. 55,75carer from one of the studies stated that support for the carers involved in conducting the research should be as robust as that for the carers participating. 107The carers in the NIHR steering group also pointed out that it is often assumed that carers do not need as much emotional support as patients.Researchers may need to show sensitivity to the impact of changing family situations, for example one researcher 52 created history profiles to avoid research demands during particularly vulnerable times.Involvement in interviewing other carers also presented challenges, triggering difficult emotions or dilemmas regarding disclosure. 32Many studies found that BOWNESS ET AL.
| 21 of 30 involving carers in groups created effective peer support systems for when issues during the research arose. 90ident in the review was the need to involve carers in ways that suited them.Many carers found virtual methods helpful, such as online meetings or editing study material through emails. 78These allowed them to remain on hand if their family members needed them 74 or fit involvement around their other responsibilities.
However, sometimes virtual meetings were less effective in establishing relationships and felt less meaningful. 80p.1226In the same way that carers are well-placed to understand the needs and preferences of participants, researchers achieved convenient involvement by designing this with carers themselves.This was achieved either through consultations before the project 67 or from the beginning, allowing the group to determine times, location, or length of meetings. 77'Having ongoing conversations with those contributing to the PPI about their experiences of the process and how they feel it could be improved enabled us to refine the process as it evolved and learn from our mistakes' (academic researcher). 126,p.985

| Carers create change
Few papers reported the carers' motivations to take on their roles in the research.Yet, a common theme was their desire to make a difference and to feel 'like our family's experience could be of some help to other families in the future' (carer). 110p.1041Thus, researchers must update carers on the study progress. 136p.11This could be provided by an end product to carer involvement, 59 such as an exhibition or new intervention.The carers in the NIHR steering group reflected on their disappointment when they felt researchers had just moved on after the project.p.25 Participatory research influenced developments in healthcare to ensure 'the concerns and issues of families at its centre', 94,p.12 with higher feasibility 58 and sustainability. 114p.5This was effectively communicated to services when carers partook in dissemination and presentations. 74To effect change, services and key stakeholders must be included in the research process. 142p.225During the process they formed networks to share knowledge and caring strategies. 90,94,123Participatory data collection methods, such as photovoice 47 and bodymapping, 74 provided opportunities to communicate a collective carers' voice.p.94p.274

| DISCUSSION
This review summarized peer-reviewed publications and grey literature that described participatory approaches involving carers in the research process, and synthesized the reported methods, benefits, challenges and facilitators of these collaborations.
As with previous reviews of other public involvement, 155 included studies used a range of designs (with the majority being qualitative), and involved carers across different stages of research.
Participatory approaches were most frequently found in research with carers for those with dementia, intellectual disabilities, paediatrics or palliative care.Perhaps this is because carers are involved more when researchers deem patients to lack capacity, or because people are less likely to identify themselves as or be recognised as 'carers' in other areas of health. 156ere were similarities in the benefits of involving carers in research to those established for participatory research approaches generally 157 ; improved the quality of research, healthcare, and increased impact for those directly involved in the process and their wider communities.Characteristics of successful involvement were similar to the recommendations from guidance for wider PPI. 158,159r example, authors attended to 'principles' (such as equality, transparency, and sensitivity) and 'presence' (by including multiple and diverse carers), echoing the 4PI National Involvement Standards. 159Best practice that was infrequent in research with carers was their involvement throughout the project.Often, researchers stated they were not able to work with carers as much as or in the ways they would have liked to, due to the contextual factors limiting opportunity for coproduction 160 (discussed below).This review attempts to highlight some of the principles that may be especially important when working with carers, which can subsequently be prioritised if compromises are required in the extent or practicalities of the participatory approach.
Carers have limited time and busy lives.The burden of research for carers was ameliorated in ways like introducing flexibility and choice into the research schedule and carers' roles.However, these approaches were sometimes potentially less effective in building relationships with or empowering the carers involved.Perhaps the key recommendation was to allow carers themselves to design how they would like to be involved and to evaluate this with them throughout the process (although only a minority of studies did this).
Another vital element to successfully involving carers was taking an action-oriented approach and maximizing the impact carers' contributions have.Carers' commitment to improve care was reported repeatedly, which motivated them to overcome some of the challenges faced during their involvement. 83In previous research, carers reported reluctance to join PPI groups because they felt their previous research encounters had not resulted in meaningful change. 23Involving carers in projects with direct outcomes and communicating their impact to carers is essential.
This review found that carers commonly contributed in the design and interpretation, and dissemination stages of research, while involvement in data collection or topic identification was rarer.As with wider forms of participatory research, 161,162 the bureaucratic barriers, funding constraints, technical requirements and traditional assumptions and hierarchies detracted from full collaboration with carers.Involvement defined as 'carer-controlled' was scarce, and some carers reported feeling their involvement was tokenistic.
Attention to the impact wider systems have on power dynamics during carer involvement was crucial, especially because carers may come to the research feeling their voice has been unheard, undervalued and considered inferior by healthcare professionals in the past. 163To facilitate meaningful engagement, researchers made efforts to increase carers' agency and prioritized building relationships.Successful partnerships with carers through research initiated far-reaching rewards, leading to ongoing reciprocal learning, trust, engagement of the wider community, and sustainable interventions. 55,114,142Unfortunately, most studies struggled to involve carers from diverse backgrounds, despite a recognition of the importance of intersectionality of caring experiences. 164Often researchers reported that this was due to the systematic barriers described above, intensified when attempting to include carers from marginalized groups.Wider institutional understanding and support is required to provide the financial resources and opportunities that communicate to carers the value of their contributions 90,165 and fulfil the emancipatory potential of participatory research. 163,166is review found diverse and inconsistent descriptions of carer involvement, and a lack of clarity around terminology persists. 157This search found studies claiming to use participatory methods where carers had only piloted materials or participated in interviews, corroborating worries that terms such as coproduction are being misused and diluted. 167Many of the papers lacked an explicit rationale for participatory approaches, needed to guide decisions regarding the practicalities of involvement 166 and ensure that carer input is maximally effective.The PAR studies in this review tended to follow a more consistent structure, with more explicit theoretical groundings and methodologies, which other involvement approaches could learn from. 1680][171] Although many studies found in this review reflected on their participatory approaches, very few conducted explicit evaluations with carers themselves.A further concern was the frequency of papers without any description of the challenges they encountered during involvement.p.162but engagement with these issues is needed to improve practice.Clearer definitions, rationale and fuller reporting of carer involvement would better allow external scrutiny through systematic assessment of the quality of their participatory methods (a challenging aspect of this review).This would ensure researchers were held accountable, 78 better credit carers for their contributions, and enable other researchers to form research-based knowledge of 'what works' within different contexts. 173Recent years have seen the development of guidance for reporting the involvement process (GRIPP 2 174 ), which may help to address this issue.Arguments for measuring the impact of public involvement, and tools for doing so, 175 have been put forward as a means of providing research-based justification for the significant time, resources and systematic changes that will be required to enable more equal research partnerships. 95,171,174e comparison stage of the narrative synthesis process. 42vealed the potential influence of the context of the report and who wrote it.The fact that the search found many instances of participatory approaches with carers that were only available as conference abstracts or protocols could suggest barriers for completing or publishing these.Peer-reviewed journal articles either included in-depth discussion of the themes or very little, likely due to differing focuses within restricted wordcounts.This lack of description of the involvement process was more common amongst studies that demonstrated higher quality research, perhaps because reporting traditional methodological rigour compromised space to reflect on the participatory process.Meanwhile, papers dedicated to discussing their participatory approach achieved more exploratory depth and provided more practical recommendations.Involving carers in the writeup is another way in which papers developed more reflective and insightful accounts of their participatory approaches.More papers reflecting on the participatory processes and increased coauthorship would be helpful in future to develop good practice for involving carers (Table 4).

| Strengths and limitations
There was a generally high consensus in the issues and recommendations authors discussed about involving carers.The majority of studies were of high research quality, but this was not the case for the quality of the involvement, which limits the robustness of the recommendations drawn.However, studies rated as having higher quality involvement are likely to have had more influence over theme development, 176 and indeed the studies with lower quality involvement were less likely to reflect on the challenges and practicalities of participatory research.Moreover, the carers who were consulted about the findings generally felt the review aligned with their views and experiences.
The challenges faced conducting this review were similar to those highlighted by previous reviewers of participatory research and PPI. 2 Due to the lack of consistent definition and reporting of public involvement, it was difficult to design a search strategy that would identify all the relevant literature within a practical scope for screening.The likelihood that this review missed potentially eligible studies remained high, as multiple studies were found through backward citation searching and expert recommendations.Some bias may have been introduced during the selection process, for example, BOWNESS ET AL.
| 23 of 30 judgement was required to determine what was research 'with' carers. 38,177There were additional challenges to determining whether carers were the majority (such as researchers not reporting the number of carers or their own identification as a carer, and the fluidity of carers' PPI membership).
The huge diversity of studies in this review is a strength, but created numerous challenges.A narrative synthesis approach incorporated difference through flexibility and multiple stages, but the process must be clearly documented. 42Theoretical frameworks can structure this interpretive process, 176,178 but the range of methodologies included in this review made it difficult to select models or quality assessment tools that suited all of these approaches.For example, categories in the 'levels and stages of user involvement' 43 was difficult to apply to photovoice, and the MMAT 41 T A B L E 4 Recommendations for facilitating effective carer involvement.

Building trusting relationships
Engage with carers' communities and existing carer organisations.
For example, involve members of these communities as facilitators, those communities, utilize existing engagement partnerships.
Maintain continuous communication-particularly relating to impact of carers' involvement and outcomes of their suggestions.
For example, carer-led newsletters throughout project, regular meetings, availability for ad-hoc conversations, tailored communication methods.
Create informal engagement opportunities (small and face to face helps).

Empowering participatory approach
Involve multiple carers.This can balance power dynamics in groups, and create ongoing peer support and advocacy groups.
Provide training and accessible methods of engagement.
For example, provide information in advance and in different formats, avoiding jargon.
Communicating value of lived experience.
Ensure institutional support.This will allow thorough supervision, planning, resources, involvement of senior academics in process.Create wider understanding amongst the whole team of the value of lived experience, wider understanding within governance structures of public involvement and a wider appreciation of time and funding requirements.
Create clear roles and expectations.

Feasible participatory approach
Provide substantial and personalised practical and emotional support to carers involved.
Design the involvement strategy with carers.
For example, ask an advisory group before, meeting at the start (when and how they would like to be involved, lengths of meetings, communication strategies), or ask those involved at the start of the partnership.
Offer a multiplicity and variety of ways for carers to be involved.
For example, online, arts-based.
Use carers time efficiently.
Work flexibly and build in ongoing review of the process.

Increasing impact of the project
Also involve stakeholders such as healthcare providers.
For example, involve professionals too in the research,.create opportunities for carers to directly feedback/disseminate to stakeholders.This allows effective care relationships to develop.
Involve carers in creation of a tangible end product.
Support capacity building and future opportunities for carers.
For example, conference attendance, ongoing advocacy roles.

Encouraging future best practice
Consistent and transparent reporting of participatory approaches.
Terminology for approach, structure of the report, include the reflections of carers involved, described the challenges and failures of participatory approaches.
a There are numerous other benefits to these approaches and strategies (not just one), as the positive effects are interrelated and amplifying.
seemed to poorly capture quality in action research.A wide variety of carers, of different ages, cultures and supporting those with very different health conditions, were included (although diversity of carers within each study was lacking).However, it is important to acknowledge many others are providing care in circumstances not captured by the definition of carer used for this review. 179While this review attempts to draw out common themes, caution should be taken if generalizing these beyond the original context of each study (as with all conclusions from qualitative analysis 176 ).Significant gaps in the literature remain where participatory approaches have not been applied, and learning from these instances would strengthen recommendations.
Finally, an important caveat to these recommendations is that systematic reviews summarize what the literature portrays, which may not reflect lived experiences of public involvement.Critical appraisal of the quality of the participatory approach for each paper also relied on author reporting, usually lacking the crucial perspective of the carers involved. 8Attempts were made to reveal the effects of reporting context by exploring differences in studies where carers were coauthors, and by incorporating the reflections of those with lived experience of involvement in research as carers to develop the final recommendations.The findings also resonated with studies that directly investigated carers' perceptions of research involvement. 180,181However, the limited influence of carers during the research process of this review is a critical weakness.Thus, these recommendations Table 4 should be taken as general principles that should be applied according to individual contextual factors.There were many similarities found in the benefits, challenges and facilitating factors to those of general public involvement, but carer-specific recommendations were also evident.

| CONCLUSION
Carers and researchers call for increased recognition of carers' value in research, and their distinct representation from patients and the public. 182Together with the NIHR's recently published resource of tips for researchers working with carers to conduct research, 183 this review hopes to encourage and inform future carer involvement in research.However, wider institutional change is also required to maximise the full emancipatory potential of participatory approaches.
photovoice (seeTable 2 footnote).The carers from the NIHR steering group queried how the context of the publication of the papers may one of these was a new publication associated with an already included reference.Studies were frequently excluded because carers were not the majority of lay members involved (n = 159), only involved in intervention design (n = 57), or not at all (n = 53) (despite participatory claims, carers were only member-checking results, piloting material, F I G U R E 1 PRISMA flow diagram depicting references screened and reviewed, in initial and updated search (templates from 44 ).
This is the first review of participatory research and public involvement, specifically with carers, finding 55 examples.Carer involvement was successful across varied study designs and contexts, consistently adding value to healthcare research, while empowering carers and engaging their wider communities.Although many examples of strategies for overcoming the potential challenges of participatory approaches with carers are presented, achieving quality in public involvement depends on dynamic and relational factors.
Where carer involvement in the research stage is separate to and sometimes overruled by researcher involvement (e.g., in photovoice analysis). 37